This invention relates to hydrothermal processing of a raw grain composition, and particularly to generation of steam suitable for use in processing grain. More particularly, this invention relates to an apparatus and a method for supplying steam to process a raw grain composition.
Grain and other starch-containing material have been processed for centuries to allow starch, which is a major nutritional component of grain, to be digested more readily by animals and humans. Currently, most industrial grain-processing methods treat a raw grain composition in either a steam chest or a pellet-mill conditioning chamber with either hot or cold water, dry heat, or steam or a combination of water, heat, and steam to gelatinize and plasticize the raw grain composition somewhat to provide a partly-processed grain composition.
Typically, operators of grain-processing systems determine the moisture content of the raw grain composition to be processed and then add a predetermined amount of moisture and heat to process the raw grain composition to produce a grain product. However, most of the moisture applied to this raw grain composition coats the surface of grain particles in the raw grain composition, and little of the moisture is actually absorbed into interior regions of the grain particles. Often too little or too much moisture is added inadvertently to the raw grain composition during conventional processing because little attention has been focused on the amount of moisture absorbed by the grain particles.
If insufficient moisture is absorbed by the grain particles, the raw grain composition used to make grain food product is not sufficiently plastic; food production costs escalate, and product quality decreases. For example, when a raw grain composition is processed in a pellet-mill conditioning chamber, the resulting partly-processed grain composition is forced through small orifices in a pellet-mill die to provide a pelletized product. A dry grain composition, i.e., one that is not sufficiently plastic, can not be forced easily through the orifices in the pellet-mill die. Additional energy and, therefore, additional costs are required to force the dry grain composition through the orifices in the mill die. Furthermore, the abrasive nature of a dry grain composition wears out the pelletizing equipment much faster than a partly-processed grain composition that is sufficiently plastic. Forcing the dry grain composition through the orifices in the pellet-mill die can overheat the dry grain composition and provide a pelletized product having an undesirable glazed surface.
A raw grain composition that includes whole grain kernels can be processed in a steam chest; the resulting partly-processed grain composition is then forced between two large rollers in a flaking mill to produce a grain flake. A dry grain composition will not be sufficiently plastic and will be crushed between the two large rollers in the flaking mill. Whether the feed product is a pellet or a flake if it is too dry, it crumbles producing fines, which are not eaten by animals.
Conversely, if too much moisture is added to the raw grain composition during processing to increase the plasticity of the partly-processed grain composition, the pellet mill becomes clogged with a wet grain composition that hydroplanes on the rollers in the mill. Grain processing must be halted while the pellet mill is cleaned out. In addition, when the wet grain is used to prepare a feed product, the resulting feed product molds before it can be consumed.
According to the present invention, a method is provided for hydrothermal processing of a raw grain composition for production of food or animal feeds. The method includes the steps of contacting a raw grain composition in a conditioning chamber with steam produced from boiler water in a boiler and delivered through a conduit including a pressure-reduction valve and through a steam inlet on the conditioning chamber. The method further includes the step of selecting the pressure-reduction valve to reduce the pressure in the conduit downstream of the valve to a value of no less than 30% of the boiler pressure. The method also includes the step of sizing the conduit so that stoichiometric amounts of steam can be delivered to the conditioning chamber at a linear velocity in the conduit of less than about 12,000 feet per minute measured downstream of the pressure-reduction valve.
In preferred embodiments, quality steam is generated in a steam supply system and delivered to a raw grain composition in a grain conditioning chamber. The steam supply system includes a water-purifier system for providing purified water to the boiler. The boiler is operated at reduced pressure to provide non-superheated steam at the reduced pressure that is delivered through a conduit coupled to the grain conditioning chamber containing the raw grain composition. The conduit further includes a pressure-reduction valve that is selected to minimize the reduction of the steam pressure in the conduit to provide non-superheated steam to the conditioning chamber. The steam generated by the steam supply system is delivered to the conditioning chamber at a low velocity to process the raw grain composition uniformly.
The steam-generating system provides steam that is essentially free of steam-borne contaminants and condensate. A water-purifying system reduces contaminants from the existing water supply and provides purified boiler water to the boiler. Steam generated from purified boiler water is free of steam-borne contaminants, so that steam supplied to the conditioning chamber consists essentially of water vapor saturated steam.
Non-superheated steam is delivered through a conduit to a grain conditioning chamber by operating the boiler at a reduced pressure. Steam of the same quality steam as that generated in the boiler is delivered to the grain conditioning chamber and used to process the raw grain composition. Delivery of this same quality steam is achieved by reducing boiler pressure and minimizing pressure reduction en route to the grain conditioning chamber. The resulting non-superheated steam enables uniform, consistency, hydrothermal processing of the raw grain composition.
Low-velocity steam is delivered to the conditioning chamber by sizing the conduit coupled to the boiler and the grain containing chamber to provide stoichiometric amounts of steam at a rate sufficient to gelatinize and plasticize the raw grain composition being fed substantially continuously into the grain conditioning chamber. The low-velocity steam allows the raw grain composition in the grain conditioning chamber to absorb essentially quantitatively all of the moisture and heat from the steam.
Additional features and advantages of the present invention will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.